Electrical filters are typically used in a circuit for filtering a power signal. FIG. 1 is a circuit block diagram of an exemplary power electronic system 100, which includes an electrical filter 102 for an inverter application arranged between a switching network 104 and a load 106. In FIG. 1, the switching network 104 is a noise source that generates a power (e.g., voltage or current) waveform containing a wanted frequency component (e.g., 50 Hz) and other unwanted frequency components (e.g., 10 kHz, 20 kHz and 30 kHz). In order to provide power signal with only the wanted frequency component to the load 106, the electrical filter 102 placed between the switching network 104 and the load 106 is arranged to allow only the 50 Hz component to be transmitted to the load. The electrical filter 102 is arranged to substantially attenuate all other unwanted frequency components, preventing them from reaching the load 106. Ideally, for the wanted frequencies, the voltage and current outputted by the filter 102 should be the same as the voltage and current inputted to the filter 102. On the other hand, for the unwanted frequencies, the voltage and current outputted by the filter 102 should be zero.
Generally, simple electrical filters for power applications comprise only passive circuit components such as resistors, inductors and capacitors. The parameters of these components are chosen based on the required filter type (e.g., low-pass, high-pass, band-pass and band-stop) as well as the required performance criteria (e.g., cut-off frequencies, quality factors). Problems associated with this type of electrical filters include their relatively bulky size; their susceptibility to filter resonance, especially when the filter is of high order; their variable cut-off frequencies, primarily due to significant tolerance of the circuit components; and their inflexibility in terms of operation.